Animal control system

ABSTRACT

An animal control system and method generates an on-off correction stimulus using a small transformer and rectifies the high voltage output to give an unfiltered unipolar voltage applied to electrodes as a correction stimulus. A small, efficient power isolation system is disclosed. An omnidirectional antenna is disclosed that reduces authentication time.

FIELD OF THE INVENTION

This invention relates to a system for controlling the behavior of ananimal.

BACKGROUND OF THE INVENTION

Animal control systems are useful to control an animal's behavior.Examples include a) containment or exclusion systems to contain ananimal within a region such as a yard or to exclude an animal from aregion such as a room, food table, sofa, bed or chair, b) trainingsystems to modify the animal's behavior, and c) bark inhibitor systemsfor dogs. The systems are usually attached to a collar for the animal. Abehavior modification signal or correction stimulus is typically anaudio sound. A stronger correction stimulus may be an electric shock.While such control systems have been miniaturized as technology hasimproved, they are still too large and too heavy for a small animal suchas a lap dog or small cat. There remains a need for control systemcircuits that minimize the number of parts and that perform functions ina different mode to permit a reduction in weight and volume.

Animal control has long been accomplished by application of electricalshock. The means for generation of the electrical shock fall into 4modes.

1 induction coil,

2 alternating current, typically with a step-up transformer,

3 direct current, typically rectified from a step-up transformer andfiltered,

4 pulse, typically by capacitor discharge into a pulse transformer

All of these approaches are difficult to miniaturize and to effect withlimited battery power while maintaining an effective stimulus. Theinduction coil mode stores energy in the coil's magnetic field, and theenergy is delivered by the collapsing inductive field. As the coil ismade smaller, less energy can be stored and the shock becomesinsufficient to control the animal.

The alternating current mode is limited to low frequencies because thephysiological response diminishes with increasing frequency. For a givenfrequency, as the step-up transformer is made smaller, it is notpossible to maintain the necessary primary inductance to keep thetransformer core from saturating, which leads to excessive currentconsumption and diminished output.

The direct current mode stores the energy on a high voltage filtercapacitor. Typically the high voltage to be stored on the capacitor isgenerated by circuitry similar to the alternating current mode justdescribed, except the high voltage is rectified either by half wave,full wave, or voltage multiplier rectification. D.C.-to-D.C. step-upcircuits are known for photomultiplier and photoflash circuits. In modemphotoflash applications a high frequency is used with a smalltransformer. A rectifier is used to supply charge to a storagecapacitor. If the circuit were to be used in an animal control system,the high voltage storage capacitor would be large and is difficult tominiaturize. The charge may also remain on the capacitor and shock theanimal at an inappropriate or unexpected time. Typically a high currentis taken from an AA size cell, which is comparatively large and heavyfor an animal control system. Further such circuits are not designed formicroprocessor control.

The pulse mode uses a pulse transformer with excellent high frequencycapability; however, the primary to secondary turns or voltage ratio islimited to low ratios in order to maintain a high self-resonantfrequency. As consequence, to achieve high voltages, a high voltage mustbe supplied to the primary. The high voltage may be supplied bycircuitry similar to the direct current mode just described and with theinadequacies just described.

Thus there remains a need for a shock system that can be controlled by amicroprocessor, is small and is operable by the limited voltage andcurrent capabilities of a small battery.

Battery powered apparatus that combines low power microprocessors withhigh power circuits, such as electronic shockers, require powermanagement because the microprocessor may malfunction if the powersupply fluctuates excessively. It is well known that the maximum poweris obtained from a source when the load is matched. This applies tobatteries as well. In a simple matched system the load resistance wouldbe equal to the source resistance, i.e. the internal battery resistance(more correctly when the source and load are conjugate impedances, butconsidering only the resistance is sufficient in this application). Insuch a system the terminal voltage of the battery drops to half the opencircuit value. Thus a 3-volt battery will drop to 1.5 volts under amatched load. Microprocessors usually fail when the supply voltage dropsby half Also the internal resistance of a battery increases near the endof battery life. Thus, even a load resistance that is higher than thenormal battery internal resistance will become significant as thebattery nears end of life. To keep the microprocessor frommalfunctioning, it is well known to isolate the microprocessor and othercircuits from temporary drops in supply voltage by using a diode feedinga capacitor, the latter maintains the voltage supplied to themicroprocessor. The typical voltage drop across a silicon diode is 0.7volts. Even Schottky diodes have 0.3 volts drop or more. This is toomuch of a voltage drop in a low voltage battery system. For example afresh 3-volt lithium battery may supply only 2.3-2.7 volts through adiode isolation circuit. This may be insufficient voltage to reliablyoperate the microprocessor. Batteries also drop in voltage near the endof battery life, and it is desirable to get maximal life from batteriesby maintaining operation even at low battery voltages. Voltage losses inload isolation systems thus reduce the amount of useful battery life.While low drop out voltage regulators are available, they do nottolerate an input voltage lower than the load voltage or consume toomuch power, compromising battery life. The usual protection scheme forthe regulator is to use a reverse coupled diode. The strategy is to dragthe load voltage down as the supply voltage drops. This protects theregulator but fails to provide the needed isolation.

Thus there remains a need for a power management system that providesisolation from transient supply voltage drops, has a minimal voltagedrop and is efficient so as to maintain long battery life.

Animal control systems that are containment or exclusion systems use anelectro-magnetic radiated signal from a boundary wire and have areceiving antenna in the form of an unshielded inductor. Such inductorshave a solenoidal reception field. Animals can learn to avoid theboundary signal by orienting themselves and, hence, the receiver to theblind spot of the solenoidal field. Simply adding another inductorphysically oriented different to the first and paralleling theelectrical circuits results in a new reception field that is the vectorsum of the two inductors, i.e. another solenoidal field. One solution isto use two or three orthogonal inductors that are activated or switchedon singly or in pairs by a controller or microprocessor, as taught inU.S. Pat. No. 5,425,330 and U.S. Pat. No. 5,435,271 to Touchton et al.The inductor or inductor pair having the strongest signal is thenselected for further signal processing. This selection process takestime. This lost time diminishes the deterrent effect for those animalsthat attempt to run through the boundary. Another solution is tosequentially sample or switch on each antenna for a period of time, astaught in U.S. Pat. Nos. 5,460,124, 5,682,839, and 6,269,776 to Grimsleyet al. The switching reduces the time the signal can be received,assuming not all three antennas are receiving sufficiently strongsignal. This reduces the ability to authenticate a weak signal becausesome of the antennas, i.e. part of the time, offer insufficient signalto process. The switching also introduces a 0.1 second latency indetecting the boundary signal as it switches through antennas that arenot receiving the boundary signal.

Thus there remains a need for an antenna system that is omnidirectionaland does not incur the lost time required for selection of the strongestsignal or is reduced in ability to authenticate a weak signal or has adetection latency.

SUMMARY OF THE INVENTION

The animal control method and system of this invention, overcomes manyof the deficiencies of the conventional animal control systems of theprior art. A particular object of this invention is achieved byinnovative circuitry, which reduces the weight and volume of the controlsystem and uses a small amount of power so that it may be applied tosmaller animals such as lap dogs and cats.

This invention provides an animal control system comprising a system toreceive a control signal such an electromagnetic boundary signal, aaudio bark signal, an ultrasonic perimeter signal, a magnetic boundarysignal, or a radio signal and to generate a correction stimuluscomprising a shock system. The shock system is typically coupled to amicroprocessor that controls the shock system. Other controllers may beused. A simple and efficient shock system comprises a correction signalgenerator coupled to a step-up transformer, the output of which iscoupled to a rectifier. The output of the rectifier is coupled toelectrodes that contact the animal to provide the correction stimulus.The correction signal generator is typically under a controller ormicroprocessor control.

It was found that alternating current frequencies above about 5kilohertz were in-sensible and hence ineffective, at least on a human.It is believed that other animals have similar frequency limits. Thus,in order to use a high frequency to permit a small transformer, it isnecessary to rectify the high voltage output. But this conventionallyrequires a high voltage filter capacitor, which is physically large.Surprisingly, it was found that the rectified high frequency voltagewithout a filter capacitor, i.e. an unfiltered unipolar high voltage,was as effective a correction stimulus as a capacitor filtered voltage.Elimination of a high voltage filter capacitor reduces the weight andphysical volume of the shock system. Rectifying means to change abipolar voltage, a voltage having both positive and negative excursions,into a unipolar voltage, a voltage having only positive or only negativeexcursions.

It is well known that smaller transformers may be used, for the samepower transferred, by raising the frequency of operation. Furthermore, alarge step-up ratio is required in order to raise a low battery voltage,such as 3 volts, to a voltage suitable for a correction stimulus, suchas 330 volts. This requires a transformer turns ratio of 1 to 110. Forexample if the primary winding requires 12 turns to achieve a sufficientinductance to keep the transformer from saturating at the operatingfrequency, the secondary winding must be 1320 turns. Such a large numberof turns will exhibit a large inductance, proportionate to the square ofthe number of turns. The otherwise small interwinding capacitanceresonates with the large inductance to give a relatively lowself-resonant frequency. Attempts to operate the transformer above theself-resonant frequency results in high losses because the secondary ofthe transformer acts as a low-pass filter. However, operation at theresonant frequency provides good low loss performance. For a small “E”core ferrite transformer, less than a centimeter on a side, with 1320turns for the secondary, the resonant frequency measured 19 kilohertz.For a small “pot” core ferrite transformer, approximately 7 millimetersin diameter, with 440 turns for the secondary, the resonant frequencymeasured 80 kilohertz. For the purposes of this invention, a highfrequency is any frequency greater than that where the physiologicaleffect of the alternating current begins to decline, i.e. above about 5kilohertz.

In order to effectively use the limited battery power available, it isuseful to maximize the physiological effect. This can be accomplished byallowing the animal's nerve endings to repolarize. Once the nerve hasdepolarized in response to the correction stimulus, further applicationof the stimulus is a waste of power. Thus it is more effective to applyan on-off control stimulus. For example, to repetitively apply a voltageof sufficient intensity and duration to substantially depolarize thenerves, then to turn the voltage off and allow the nerves to repolarizeand then to reapply the voltage, etc. It is desired to apply the voltage5 to 200 times per second. Fewer than 5 fails to impress an urgency ofresponse while greater than 200 looses the insistence of sensiblydiscrete actions. Thirty repetitions per seconds are preferred. In otherwords, the controlled on time of the stimulus signal is one sixtieth ofa second and the off time of the stimulus signal is one sixtieth of asecond, where upon the stimulus signal is again reapplied for a sixtiethof a second and so forth.

A less strong or graded correction stimulus can be achieved by reducingthe duration and/or intensity of the voltage so as to not extensivelydepolarize the nerves. For example the on time of the stimulus signalmay be reduced. To keep the perceived stimulus signal constant the offtime of the stimulus signal may be increased by the amount of time theon time is reduced, so as to keep the sum of the on time and off timeconstant.

Furthermore, a more effective correction stimulus may be created bycontinuing the correction stimulus voltage for periods of time,including the on time and off time control of the correction stimulus,then discontinuing the correction stimulus voltage for periods of time.The animal receives the aversive correction stimulus and is allowed toreact to it without being so affected as to be unable to respond to thecorrection stimulus. The stimulus may be continued or applied for 0.5 to20 seconds then discontinued or stopped for 0.5 to 20 seconds. Thecorrection stimulus may then be continued to further control the animal.Of course, the control signal should still present to continue thecorrection stimulus.

Also it may be desirable to stop the control signal all together after atime because the animal may be trapped or unable to react to the controlstimulus. For example, after 20 to 120 seconds, the correction stimulusmay be stopped for an extended time, 4 minutes or more, or until thecontrol signal is not detected, which resets the sequence of thecorrection stimulus.

A method of utilizing a small, efficient, and effective shock system foranimal control comprises a) mounting on the animal a controller toreceive a control signal, b) generating a correction signal, c) couplingthe correction signal to a step-up transformer to produce a stepped-upcorrection signal, c) rectifying the stepped-up correction signal, andd) applying the rectified stepped-up correction signal to the animal asa correction stimulus to control the animal. Mounting means to put intoproper position for use.

This invention provides a power isolation system for the low batteryvoltages commonly used, such as 3 volts, to maintain operational voltagefor the microprocessor and other signal processing circuits by utilizinga pass transistor. A FET would be ideal in terms of low voltage drop butit is symmetric so that it will conduct from the higher to the lowervoltage whether it is the power source or the load. Additional circuitryand power consumption would be required to overcome this deficiency. Abipolar transistor has a small voltage drop when saturated, about 50 to300 millivolts. The bipolar transistor is symmetric in that the emitterand collector can be interchanged. However, most bipolar transistors areoptimized for other performance characteristics and are not symmetricalin performance. It was found that high forward gain transistors (forwardcurrent gain greater than 50) tend to have a low reverse gain, (reversecurrent gain less than 1), i.e. when the collector and emitter areinterchanged. Thus a bipolar transistor with a large forward gain and asmall reverse gain can be used to supply a relatively large current fromthe power source to the load but will supply only a small reversecurrent from the load to the “source” when the source is a lower voltagethan the load voltage. With the collector connected to the load, thetransistor base current is supplied by a resistor to ground of apreferred value just sufficient in resistance to saturate the transistorin normal operation so that the voltage drop is minimized. Other sourcesof base current may be used. The base current may be fixed such thatadditional circuitry is not required, for example to turn the basecurrent on and off, to achieve the power isolation. In thisconfiguration, when the “source” voltage drops below the load voltagethe transistor is substantially non-conducting and only a small reverseor “leakage” current will flow from the load. Thus good isolation isprovided with a minimal voltage drop and with a simple compact circuit.

An animal containment or exclusion system is a particular kind of animalcontrol system that uses a boundary signal to restrict the animal toapproved regions. A boundary signal is created by applying an “RF”signal (“radio frequency” although the frequency may be as low as 7kilohertz) to a perimeter wire to radiate an electromagnetic signal thata receiver mounted on the animal can receive to activate a correctionstimulus. The boundary signal is received by an inductor and it isnecessary to use two or more inductors to overcome the blind spots inthe characteristic solenoidal receiving field of a single inductor.Connecting the inductors together will result in an equivalentsolenoidal receiving field that is equivalent to a single inductor. Thusthe blind spots will not have been removed.

It is desired to combine the signals from a plurality of inductors, eachphysically oriented in a different direction without getting anequivalent solenodial field. To do this, the axes of the inductors arephysically oriented in different directions, substantially orthogonally,and the individual received signals modified so that combining or addingthe signals does not result in an equivalent solenoidal receiving fieldor a field with nulls.

This invention shifts the electrical phase differently of the receivedsignals before combining them, particularly signals at the carrierfrequency. The combined signals do not become an equivalent solenoidalfield because signals of different electrical phase cannot cancel eachother to give a blind spot.

In a preferred embodiment two inductors receive the boundary signal, thereceived signals are shifted 90 electrical degrees relative to eachother so that they can be considered as a sine and cosine wave. It iswell known mathematically that the sine and cosine are orthogonal (notin the physically orthogonal sense above) and cannot cancel each other.However, any electrical phase shift greater than about 45 electricaldegrees will substantially eliminate the signal cancellation thatresults in nulls or an equivalent solenoidal field of response, providedthat the inductors are oriented differently. Shifting the relativeelectrical phase 135 degrees gives performance similar to that of 45degrees but as if one of the inductors were physically inverted.

In a preferred embodiment two inductors receive the boundary signal, thereceived signals from each inductor are amplified and the amplifier isconstructed to shift the electrical phase of the signal. The twoamplifiers are constructed to shift the phase differently. It ispreferred that the phase is different by at least 45 electrical degreesand 90 degrees is more preferred.

It is common to use the inductor as part of a tuned circuit that isresonated by a capacitor to a frequency matched to the boundary signalfrequency, also called the carrier frequency. This is advantageousbecause interfering signals can be rejected. A high “Q” (“qualityfactor” affecting the width of the frequency response)inductor-capacitor circuit may be used to further reject interferingsignals. In a preferred embodiment of this invention, at least one oftuned circuits is tuned slightly away from the boundary signal frequencyso that the electrical phase of the received signal is shifted.

In a preferred embodiment two inductors are substantially physicallyorthogonal and the electrical phase of the received boundary signalsoutputted by the inductors are shifted by tuning a first inductor and afirst capacitor and second inductor and second capacitor to frequenciesabove and below the carrier frequency, respectively, so that theelectrical phase difference between them is greater than 45 degrees,preferably 90 degrees. Tuned above means the resonant or most sensitivefrequency of the inductor and capacitor is greater than the carrierfrequency, and analogously for tuned below. The Q may be modified byshunting the inductors with resistors.

With only two inductors and with phase-shifted signals, a null in thereceived signal still remains in one plane. Use of three inductorsoriented in three different directions will eliminate the nullaltogether. In a preferred embodiment three inductors are substantiallyphysically orthogonal and receive the boundary signal the receivedsignals are shifted 60 electrical degrees relative to each other.However, any electrical phase shift greater than about 30 electricaldegrees but less than about 90 degrees will substantially eliminate thesignal cancellation that results in blind spots in the field ofresponse.

In a preferred embodiment three inductors are substantially physicallyorthogonal and receive the boundary signal, the received signals fromeach inductor are amplified and the amplifier is constructed to shiftthe electrical phase of the signal. The three amplifiers are constructedto shift the phase differently. It is preferred that the phases aredifferent from each other by 60 electrical degrees. The inductors mayalso be resonated with capacitors and the Q adjusted with resistors.

In a preferred embodiment the electrical phase of the received boundarysignals are shifted by tuning a first inductor and a first capacitor anda third inductor and a third capacitor to frequencies above and belowthe carrier frequency, respectively, so that the electrical phasedifference is 60 degrees and tuning a second inductor and secondcapacitor to the carrier frequency. The sensitivity of second inductorand second capacitor may be matched to that of the others at the carrierfrequency.

A method of animal control utilizing an antenna system for animalcontainment which does not need switching, does not give upauthentification of weak signal, has no latency, and has fewer or nonulls in the response field comprises the steps: a) mounting on ananimal a receiver to receive a boundary signal, b) receiving theboundary signal with a plurality of receiver subsystems, each havingsubstantially orthogonal physical axes, c) shifting the electrical phaseof the received boundary signals, forming shifted received boundarysignals, d) combining the shifted received boundary signals, e)detecting the combined shifted received boundary signals and f)generating a correction stimulus to control the animal.

The phase shifting also may be accomplished by tuning the inductor andcapacitor and phase shifting by the amplifier.

BRIEF DESCRIPTION OF THE DRAWINGS

The following description of this invention will be better understoodwhen read in conjunction with the accompanying drawings in which:

FIG. 1 is a partial schematic drawing of a shock system;

FIG. 2 is a partial schematic drawing of a power isolation system;

FIG. 3 is a partial schematic drawing of a boundary signal receiver;

FIG. 4 is an illustration of signals with differing phase,

FIG. 4a is an illustration of the combining of signals with differingphase;

FIG. 4b is an illustration of the combining of signals with differingphase;

FIG. 5 is a partial schematic drawing of an alternate boundary signalreceiver; and

FIG. 6 is a graph of phase and amplitude responses of a three tunedcircuit antenna.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The shock system of this invention is better understood by reference toFIG. 1 in which a partial circuit is drawn. The controller 101, possiblya microcomputer, receives a control signal, not shown, and commands acorrection stimulus to be generated by dropping the voltage on wire 102from a value near the supply voltage indicated as ++, to zero volts.Wire 102 is connected from the controller 101 to the emitter of NPNtransistor 105. Lowering the voltage on the emitter causes current toflow in the transistor's base from the supply voltage through resistor103. The base current is increased by the gain of transistor 105 andflows from the collector through resistor 104 to the base of PNP powertransistor 106. Transistor 106 amplifies the base current to flow fromits collector through the primary winding of step-up transformer 107.The current in the primary of transformer 107 creates a primary voltageand is coupled to its secondary to give a much larger voltage. Thesecondary of transformer 107 is coupled to fast recovery rectifier 108,the other side of which is connected to one of the stimulus electrodes111 for applying the correction stimulus to the animal. The otherstimulus electrode 111 is connected to ground or common to complete thecircuit. The others side of the secondary is connected to the base oftransistor 105. Also connected to the base of transistor 105 iscapacitor 109 the other side of which is connected to ground. Capacitor109 is selected during design to adjust the phase of current throughtransistor 106 relative to the voltage across transformer 107, toimprove the efficiency of power conversion.

Surprisingly it was found that good physiologic response was generatedwithout using an output storage or filter capacitor across stimuluselectrodes 111. However, a small capacitor might be placed across thestimulus electrodes 111 to protect the circuit from static electricdischarges. But it is preferred to keep the capacitance across theelectrode to a minimum, less than about 10 nanofarads, to allow rapidbuild up and decay of the correction stimulus voltage. The correctionstimulus voltage should decay more than 50% during the off time of theon time/off time sequence.

In a preferred embodiment, the transformer 107 was a 8.3 mm wide by 8 mmhigh by 3.6 mm wide ferrite “E” core with 12 primary turns and 1320secondary turns, for a voltage step-up of 110. With a supply voltage of3 volts, from a lithium battery not shown, nearly 300 volts is outputfrom the transformer 107 depending on the degree to which the voltage ofthe battery is diminished by the heavy load of the shocker. Componentwere 103, 10,000 ohms; 104, 100 ohms; 105, 2N3904; 106, FMMT591A; 108FR16; and 109, 1000 picofarads. In a preferred embodiment, an evensmaller transformer 107 was a 7 mm diameter by 4 mm high ferrite potcore with 4 primary turns and 440 secondary turns.

The power isolation system of this invention is better understood byreference to FIG. 2 in which a partial schematic circuit is drawn. Thebattery, not shown, supplies a voltage (indicated as ++) to input wire201. The wire is connected to filter capacitor 202 and to the emitter ofbipolar PNP transistor 205. The base of transistor 205 is connected toground through resistor 203. The collector of transistor 205 isconnected to storage capacitor 204 and output wire 207. NPN transistor206 is diode connected with its collector and base connected to inputwire 201 and its emitter connected to output wire 207. In operationdiode connected transistor 206 supplies current to the output from theinput when the battery is first connected to give a rapid voltage riseas required for some microcomputers. But since the voltage drop acrosstransistor 206 is about 0.7 volts, transistor 205 supplies additionalcurrent to charge the output capacitor 204 to with in about 80millivolts of the input voltage. The current flowing at the base oftransistor 205 through resistor 203 is small, fixed or nearly constant,about 1 microamp. Because the gain of transistor is chosen to be high,the collector is saturated giving a low emitter to collector voltage.The diode-connected transistor could be eliminated if there is no needto rapidly charge capacitor 204. Considering the currents of typicalanimal control systems, a diode such as a 1N4448 could be used in placeof the diode-connected transistor.

The component values were; 202, 440 microfarad; 203, 2 megohm; 204, 220microfarad; 205, 2N5087; and 206, 2N3904.

With 3 volts on wire 201, the initial current supplied to 207 at groundpotential by transistor 205 without 206 in the circuit was 400microamps. With 3 volts on wire 207 and zero volts on 201, the reversecurrent through transistor 205 was 4 microamps, i.e. substantiallynonconducting. With the voltages used in this application, the forwardto reverse gain of the transistor is 100:1. In normal operation, with 15microamps drawn from 207, the voltage drop across transistor 205 was 80millivolts after charging 204.

A preferred receiver of this invention is better understood by referenceto FIG. 3 in which a partial circuit is drawn. The first antenna system10 comprises the inductor 11, capacitor 12, and resistor 14 connected inparallel to selectively receive the boundary signal carrier frequency.The output of circuit 10 is coupled through capacitor 15 to the base oftransistor 334. The second antenna system 20 comprises the inductor 21,capacitor 22, capacitor 23, and resistor 24 connected in parallel, toalso selectively receive the boundary signal carrier frequency. Theoutput of circuit 20 is coupled through capacitor 25 to the base oftransistor 334. The third antenna system 30 comprises the inductor 31,capacitor 32, capacitor 33, and resistor 34 connected in parallel, toalso selectively receive the boundary signal carrier frequency. Theoutput of circuit 30 is coupled through capacitor 25 to the base oftransistor 334. The inductors are drawn in different orientations torepresent the different physical alignments of the physical devices thatare preferably physically orthogonal. The collector of transistor 334 isconnected to a supply voltage, not shown, through resistor 331. Theoperating base current is supplied by resistor 332, connected betweenthe base and collector of transistor 334. The cathode of diode 333 isconnected to the base of transistor 334 and the anode to ground. Diode333 protects transistor 334 from excessive reverse voltage when theinductors are very near a boundary wire and the signal is very large.The signal amplified by transistor 334 is coupled to additionalconventional and known in the art circuitry, not shown, by capacitor 335connected to the collector of transistor 334.

Components were; 11, 32 millihenry; 12, 6.8 nanofarads; 14, 68 kiloohms;15, 100 picofarads; 21, 32 millihenry; 22, 6.8 nanofarads; 23, 330picofarads, 24, 33 kiloohms; 25 100 picofarads; 31, 32 millihenry; 32,6.8 nanofarads; 33, 680 picofarads, 34, 68 kiloohms; 35 100 picofarads;331, 470 kiloohms; 332, 2 megohms; 333, 1N4448; 334, 2N5089; and 335,220 picofarads.

The phase of the received boundary signal is affected by the resonantcharacteristics of receiving antennas 10, 20, and 30. In a preferredembodiment, antenna 10 is tuned above the boundary signal carrierfrequency, 10.6 kilohertz. Antenna 20 is tuned to the boundary signalcarrier frequency by the addition of capacitor 23. Antenna 30 is tunedbelow the boundary signal carrier frequency by the addition of capacitor33. The resistors 14, 24, and 34 control “Q” of the resonant circuits.Resistor 24 also affects the sensitivity of antenna 20 and can be usedto match it to antennas 10 and 30 for reasons illustrated in FIG. 6. Thevalues of resistance are chosen to allow normal manufacturing tolerancecomponents to be used and still operate according to this invention.Other means may be used to affect the difference in the tuning. Forexample the value of the inductors might, be made different. Instead ofparalleling capacitor 23 across capacitor 22, a different value ofcapacitor 22 might be chosen eliminating the need for capacitor 23, andsimilarly for capacitor 33.

FIG. 4 illustrates three received signals with differing phase. Ifsignal 402 is taken as zero degrees phase (electrical), then 401 is −60degrees and 403 is +60 degrees. While 401 and 403 are 120 degreesdifferent as drawn, it is recognized that for example 401 might benegative in amplitude in which case 401 and 403 would equivalently be 60degrees different rather than 120 degrees. The amplitudes of the signalsvectors are drawn as equal in magnitude. As can be seen, for threeantennas, the 60 degrees phase difference distributes the phasedifferences optimally. Of course, the amplitudes will in general bedifferent in use depending on the orientation of the physical antenna tothe boundary signal. Also the amplitude and phase depends on the exactvalue of the components.

FIG. 4a illustrates the vector resultant of adding equal amplitudesignals from 402 and 403 of FIG. 4 as occurs when 402 and 403 are each45 physical degrees to the boundary signal. The resultant 405 is greaterin amplitude than either of the individual signals.

FIG. 4b illustrates the vector resultant of adding equal amplitudesignals from 402 and 403, except the latter's amplitude is negative. Anegative amplitude is equivalent to a 180-degree shift and naturallyoccurs if the winding sense of the inductor is reversed or if thereceiver is turned 180 degrees about an axis associated with the antennaproducing signal 402. The resultant 406 is approximately equal inamplitude to the individual signals but somewhat less than that of 405.It is important to note that there is no orientation, which will producea null, unlike a single antenna. While the resultant amplitude may varysome depending on the orientation, the distance at which the boundarysignal is detected is not significantly different.

Best performance is achieved with the phases conform to the above,however the actual phase may be more or less and achieve the eliminationof nulls in the response. In the case of 2 inductors the phasedifference may be from about 45 to 135 degrees. In the case of threeinductors the minimum phase difference may be from 30 to 90 degrees.

Best performance is achieved with the inductors physically orthogonal(90 degrees) to each other. Substantially physically orthogonal meansthe orientation of any 2 inductors may be from 45 to 135 physicaldegrees and still permit the effective elimination of nulls from thereceiving field.

A preferred embodiment is shown in FIG. 5; the antennas 510, 520, and530 are coupled to individual amplifiers. The antenna 510, comprisingthe parallel components inductor 511, capacitor 512 and resistor 514, iscoupled by capacitor 515 to the base of transistor 554. The collector oftransistor 554 is connected to a power source through resistor 551.Resistor 552 is connected between the base and collector of transistor554 to provide operational base current. Diode 553 is to protecttransistor 554 from excessive reverse voltage. Capacitor 555 couples theamplified signal to wire 580 that conveys the signal to other common andknown in the art circuit circuitry, not shown. The antenna 520,comprising the parallel components inductor 521, capacitor 522 andresistor 524, is coupled by capacitor 525 to the base of transistor 564.The collector of transistor 564 is connected to a power source throughresistor 561. Resistor 562 is connected between the base and collectorof transistor 564 to provide operational base current. Diode 563 is toprotect transistor 564 from excessive reverse voltage. Capacitor 565couples the amplified signal to wire 580 that conveys the signal toother common and known in the art circuit circuitry. Capacitor 566causes a lag in the phase of the signal. Making the value of capacitor555 smaller than 565 causes a relative lead in phase of the signal from510. The antenna 530, comprising the parallel components inductor 531,capacitor 532 and resistor 534, is coupled by capacitor 535 to the baseof transistor 564. The collector of transistor 574 is connected to apower source through resistor 571. Resistor 572 is connected between thebase and collector of transistor 574 to provide operational basecurrent. Diode 573 is to protect transistor 574 from excessive reversevoltage. Capacitor 575 couples the amplified signal to wire 580 thatconveys the signal to other common and known in the art circuitcircuitry. The sensitivity or gain of 530 and its amplifier (574) needsto be lower that that of 510 and 520 and their amplifiers (for reasonsillustrated in FIG. 6) this may be accomplished with, for example,selected values of resistor 534 or resistors 571 or 572. This circuitconfiguration can utilize a narrower antenna resonance, i.e. higher Q,for a given component tolerance than the circuit of FIG. 3 and eliminatepotential interfering signals. The antenna and the associated amplifieris a receiver subsystem.

Components were; 511,521,531, 33 millihenry; 512,522,532, 6.8nanofarads; 514,524,534, 100 kldoohms; 515,525,535, 100 picofarads; 551,470 kiloohms; 552, 2 megohms; 553, 1N4448; 554, 2N5089; 555, 220picofarads; 561, 470 kiloohms; 562, 2 megohms; 563, 1N4448; 564, 2N5089;565, 1000 picofarads; and 566, 150 picofarads; 571, 470 kiloohms; 572, 1megohm; 573, 1N4448; 574, 2N5089; 575, 1000 picofarads.

FIG. 6 illustrates the phase and amplitude response with antennacomponent values of the preferred embodiment of FIG. 3. The amplituderesponse 610 to frequencies received by antenna 10 shows a peak responsedefined as 100 near 10.9 kilohertz and 55 at the carrier frequency 601.Antenna 10 shows a phase response 611 of approximately +60 degrees atthe carrier frequency 601. The amplitude response 620 to frequenciesreceived by antenna 20 shows a peak response of approximately 55 at thecarrier frequency 601, 10.62 kilohertz. Antenna 20 shows a phaseresponse 621 of approximately zero degrees at the carrier frequency. Theamplitude response 630 to frequencies received by antenna 30 shows apeak response of 100 near 10.4 kilohertz and 55 at the carrier frequency601. Antenna 20 shows a phase response 631 of approximately −60 degreesat the carrier frequency 601. The circle 602 is meant to draw attentionto the operational region of the drawing where the three antennas are ofapproximately equal sensitivity, within the variances of normalproduction components.

With the teachings of this invention, it will be apparent to thoseskilled in the art as to how to change the components for differentapplications, such as carrier frequency or greater sensitivity withhigher inductance antennas.

I claim:
 1. An animal control system to contain within or exclude from aregion comprising: a receiver to receive a boundary signal having acarrier frequency and to control the animal, the receiver comprising;(a) a plurality of substantially physically orthogonal antenna systemsfor receiving the boundary signal, (b) each antenna system having adifferent electrical phase, (c) a combiner for combining the receivedboundary signals, and (d) a stimulus generator to control the animal. 2.The system of claim 1 wherein: each antenna system comprises; aninductor and a capacitor tuned to receive to the boundary signal andeach antenna outputting a different electrical phase.
 3. The system ofclaim 2 wherein a first inductor and a first capacitor are tuned abovethe carrier frequency and a second inductor and a second capacitor aretuned to the carrier frequency and a third inductor and a thirdcapacitor are tuned below the carrier frequency to cause the electricalphases to be different.
 4. The system of claim 3 wherein the firstinductor and the first capacitor are tuned above the carrier frequencyby an electrical phase of 60 degrees and the third inductor and thethird capacitor are tuned below the carrier frequency by a phase of 60degrees.
 5. The system of claim 2 wherein a first inductor and a firstcapacitor are tuned above the carrier frequency and a second inductorand a second capacitor are tuned below the carrier frequency to causethe electrical phases to be different each from the other.
 6. The systemof claim 5 wherein the first inductor and the first capacitor are tunedabove the carrier frequency by an electrical phase of 45 degrees and thesecond inductor and the second capacitor are tuned below the carrierfrequency by a phase of 45 degrees.
 7. The system of claim 1 wherein:the each antenna system having a different electrical phase comprises(a) an inductor coupled to an amplifier, (b) each amplifier having adifferent phase.